The rotation portion of the rolling movement must be changed in a gear grinding machine when gears with differing diameter are manufactured. It is known for this purpose to also exchange the roll cam with a change in the diameter of the workpiece. Such an operation, however, requires a considerable amount of change-over time.
Rolling drives are known from German Patentschrift No. 7 21 899, German Offenlegungsschrift No. 27 01 204 and U.S. Pat. Nos. 3,263,372, 4,045,916 and 4,045,917. A method and apparatus for steplessly adjusting a rolling drive is already known from German Pat. No. 35 15 913, which corresponds to U.S. Pat. No. 4,739,587. The driven roll-cam carriage and the roll-band carriage are connected through joints with a rocker arm which is hinged to a part on the machine frame, which part can be adjusted in correspondence with the workpiece diameter to transmit the movement of the roll-cam carriage onto the roll-band carriage. As practice has shown, this known roll drive is, due to its kinematics, not very rigid and therefore less suited for machining of precision gears.
The basic purpose of the invention is to further develop the methodology and apparatus of this type so that a better synchronization of the translatoric movements of the roll-cam carriage and of the roll-band carriage results to bring about a precisely defined rolling movement of the roll cam.
As will yet be discussed in greater detail in connection with the description of a preferred exemplary embodiment of the invention, it is necessary during the machining of a gear, the diameter of which is larger than the diameter of the roll cam, to cause a movement of the roll-band carriage to coincide with the movement of the roll-cam carriage. This means that the speed of the roll-band carriage relative to the roll-cam carriage is always less than relative to the machine frame. Thus the movement of the roll-band carriage relative to the roll-cam carriage, that is the distance between the two carriages, can be measured substantially more exactly with an electric measuring device than the path covered by the roll-band carriage with respect to the machine frame. Since the measured values determined by a measuring device are processed in a calculator, it must also be considered that the frequency of the measuring impulses has a natural limit caused by the efficiency of the calculator. A measuring of the distance between the two carriages is also for this reason substantially more advantageous than a measuring of the path covered by the roll-band carriage with respect to the machine frame. Also errors in measurement are avoided by the inventive method, which errors result from length changes of the machine frame due to temperature variations.